Combine the olive oil, half the parsley, and the garlic in a cazuela or sauté pan large enough to hold the fish and clams in a single layer. Sprinkle the hake on both sides with salt and add to the cazuela, skin side down. Dust the fish with flour, then add the clams and ½ cup water and bring to a simmer. Cook for 2 minutes, then turn the fish, lower the heat, and simmer very gently until the clams open and the fish is cooked through, about 5 minutes. Divide the fish and clams among four plates, stir the pan juices, and spoon over the fish and into the clams. Sprinkle with the remaining parsley and serve.